Separation of 2-butanol from isobutanol by extractive distillation

ABSTRACT

2-Butanol cannot be separated from isobutanol by distillation or rectification because of the closeness of their boiling points. 2-Butanol is readily separated from isobutanol by extractive distillation. Effective agents are propylene glycol propyl ether, 2-methoxyethanol and ethyl acetate.

FIELD OF THE INVENTION

This invention relates to a method for separating 2-butanol from isobutanol using certain organic compounds as the agent in extractive distillation.

DESCRIPTION OF PRIOR ART

Extractive distillation is the method of separating close boiling compounds from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive agent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The extractive agent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive agent is introduced a few plates from the top of the column to insure that none of the extractive agent is carried over with the lowest boiling component. This usually requires that the extractive agent boil about twenty Celcius degrees or more higher than the highest boiling component.

At the bottom of a continuous column, the less volatile components of the close boiling mixtures and the extractive agent are continuously removed from the column. The usual methods of separation of these two components are the use of another rectification column, cooling and phase separation, or solvent extraction.

                  TABLE 1                                                          ______________________________________                                         Effect of Relative Volatility on Theoretical Stage                             Requirements.                                                                  Separation Purity,                                                                        Relative Volatility                                                 Both Products                                                                             1.02   1.1     1.2 1.3  1.4 1.5  2.0 3.0                            (Mole Fraction)                                                                           Theoretical Stages at Total Reflux                                  ______________________________________                                         0.999      697    144     75  52   40  33   19  12                             0.995      534    110     57  39   30  25   14  9                              0.990      463    95      49  34   26  22   12  7                              0.98       392    81      42  29   22  18   10  6                              0.95       296    61      31  21   16  14    8  4                              0.90       221    45      23  16   12  10    5  3                              ______________________________________                                    

2-Butanol and isobutanol boil ten degrees apart and have a relative volatility of 1.22 which makes it difficult to separate them by conventional distillation or rectification. Table 2 shows that with an agent giving a relative volatility of 1.6, only twenty-seven actual plates are required to get 99% purity compared to 61 plates for straight rectification.

                  TABLE 2                                                          ______________________________________                                         Theoretical and Actual Plates Required vs. Relative                            Volatility for 2-Butanol from Isobutanol Separation                            Relative                                                                               Theoretical Plates Required                                                                     Actual Plates                                         Volatility                                                                             At Total Reflux, 99% Purity                                                                     Required, 75% Efficiency                              ______________________________________                                         1.4     26               35                                                    1.5     22               30                                                    1.6     20               27                                                    ______________________________________                                    

OBJECTIVE OF THE INVENTION

The object of this invention is to provide a process or method of extractive distillation that will enhance the relative volatility of 2-butanol and isobutanol in their separation in a rectification column. It is a further object of this invention to identify effective extractive distillation agents that are stable and can be recycled.

SUMMARY OF THE INVENTION

The objects of this invention are provided by a process for the separation of 2-butanol and isobutanol which entails the use of certain organic compounds when employed as the agent in extractive distillation.

DETAILED DESCRIPTION OF THE INVENTION

I have discovered that certain organic compounds will effectively increase the relative volatilty between 2-butanol and isobutanol during rectification when employed as the agent in extractive distillation. They are benzyl acetate, ethylene carbonate, isobutyl isobutyrate, 2-octanone, cyclopentanone, 2-undecanone, isophorone, 2-butoxyethanol,2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, propylene glycol propyl ether, 1,2-propanediol, 2-methyl-2,4-pentanediol, ethyl acetate diethyl malonate, p-xylene, beta-pinene, dipentene, 1,2,3,4-tetrahydronaphthalene, dipropyl amine, N-Methylpyrrolidone, 3-dimethylaminopropylamine, N,N-diethylaniline, morpholine, pyridine, N,N-dimethylethanolamine, benzonitrile, butyronitrile, cyclohexylamine, 4-ethylmorpholine, butyrolactone, 1-nitropropane, 4-ethylmorpholine, 2-nitropropane, dimethylsulfoxide, 1,2,4-trimethylbenzene, formamide, 2,4-dimethylphenol, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, N,N-dimethylformamide, salicylaldehyde and diethylene glycol ethyl ether.

THE USEFULNESS OF THE INVENTION

The usefulness of this invention can be demonstrated by referring to the data presented in Tables 1,2 and 3. All of the successful agents show that 2-butanol can be separated from isobutanol by means of extractive distillation in a rectification column and that the ease or separation as measured by relative volatility is considerable.

WORKING EXAMPLE

1. Fifty grams of 2-butanol-isobutanol mixture and fifty grams of propylene glycol propyl ether were charged to a vapor-liquid equilibrium still and refluxed for two hours. The vapor composition was 72.2% 2-butanol and 27.8% isobutanol; the liquid composition was 61.2% 2-butanol and 38.88 isobutanol. This is a relative volatility of 1.65.

                  TABLE 3                                                          ______________________________________                                         Effective Extractive Distillation Agents For                                   Separating 2-Butanol From Isobutanol                                                               Relative                                                   Compounds           Volatility                                                 ______________________________________                                         None                1.22                                                       Benzyl acetate      1.45                                                       Ethylene carbonate  1.35                                                       Isobutyl isobutyrate                                                                               1.35                                                       2-Octanone          1.35                                                       Cyclopentanone      1.35                                                       2-Undecanone        1.35                                                       Isophorone          1.4                                                        2-Butoxyethanol     1.35                                                       2-Methoxyethanol    1.5                                                        2-Ethoxyethanol     1.5                                                        1-Methoxy-2-propanol                                                                               1.35                                                       Propylene glycol propyl ether                                                                      1.65                                                       1,2,Propanediol     1.55                                                       2-Methyl-2,4-pentanediol                                                                           1.35                                                       Ethyl acetate       1.5                                                        Diethyl malonate    1.35                                                       p-Xylene            1.35                                                       beta-Pinene         1.35                                                       1,2,3,4-Tetrahydronaphthalene                                                                      1.35                                                       Dipentene           1.45                                                       Dipropyl amine      1.45                                                       N-Methylpyrrolidone 1.4                                                        3-Dimethylaminopropylamine                                                                         1.6                                                        N,N-Diethylaniline  1.5                                                        Morpholine          1.55                                                       Pyridine            1.5S                                                       N,N-Dimethylethanolamine                                                                           1.5                                                        Benzonitrile        1.35                                                       Butyronitrile       1.65                                                       Cyclohexylamine     1.55                                                       4-Methylmorpholine  1.5                                                        Butyrolactone       1.35                                                       1-Nitropropane      1.35                                                       4-Ethylmorpholine   1.5                                                        2-Nitropropane      1.4                                                        Dimethylsulfoxide   1.45                                                       1,2,4-Trimethylbenzene                                                                             1.35                                                       2,4-Dimethylphenol  1.5                                                        N,N-Dimethylacetamide                                                                              1.45                                                       1-Methyl-2-pyrrolidone                                                                             1.4                                                        N,N-Dimethylformamide                                                                              1.5                                                        Formamide           1.45                                                       Salicylaldehyde     1.45                                                       Diethylene glycol ethyl ether                                                                      1.35                                                       ______________________________________                                     

I claim:
 1. A method for recovering 2-butanol from a mixture consisting of 2-butanol and isobutanol which consists essentially of distilling said mixture consisting of 2-butanol and isobutanol in the presence of an extractive distillation agent, recovering the 2-butanol as overhead product and obtaining the isobutanol and the extractive distillation agent as bottoms product, wherein said extractive distillation agent consists essentially of one material selected from the group consisting of benzyl acetate, ethylene carbonate, isobutyl isobutyrate, 2-octanone, cyclopentanone 2-undecanone, isophorone, 2-butoxyethanol,2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, propylene glycol propyl ether, 1,2-propanediol, 2-methyl-2,4-pentanediol, ethyl acetate diethyl malonate, p-xylene, beta-pinene, dipentene, 1,2,3,4-tetrahydronaphthalene, dipropyl amine, N-Methylpyrrolidone, 3-dimethylaminopropylamine, N,N-diethylaniline, morpholine, pyridine, N,N-dimethylethanolamine, benzonitrile, butyronitrile, cyclohexylamine, 4-methylimorpholine, butyrolactone, 1-nitropropane, 4-ethylmorpholine, 2-nitropropane, dimethylsulfoxide, 1,2,4-trimethylbenzene, formamide, 2,4-dimethylphenol, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, N,N-dimethylformamide, salicylaldehyde and diethylene glycol ethyl ether. 